The present invention relates generally to ink jet printers and more specifically to piezoelectrically driven print heads for applying ink droplets on demand to a writing surface. Exemplary of such print heads is that described in U.S. Pat. No. 3,747,120, entitled Arrangement of Writing Mechanisms for Writing on Paper with a Colored Liquid. This and other prior art relating to ink jet printers fails to recognize the need for protecting the ink supply within the print head from the effects of physical shocks to the ink supply cartridge or the ink supply tube.
One undesirable effect of the lack of shock protection is the shock induced ingestion of air bubbles into the ink supply within the print head via the discharge channel. The presence of just a single air bubble in the ink supply within the print head seriously degrades performance of the print head. Another undesirable effect of the lack of shock protection is the spurious and premature ejection of ink droplets from the print head in response to physical shocks to the ink supply cartridge or the ink supply tube.
Attempts have been made in the prior art to reduce these undesirable effects by positioning a flow restriction device in the ink supply tube to attenuate shock pulses travelling down the ink supply tube to the print head. Although this solution has been somewhat successful in attenuating shock pulses and their effects, it has the major disadvantage of causing a restriction in the normal flow of ink proportional to the amount of attenuation of the shock pulse.
The pressure pulse travelling through the ink supply tube may be viewed as the sum of a mathematical series of sinusoidal pressure variations within the ink while the normal ink flow may be viewed as a non-varying, or DC, term. It would, therefore, be advantageous to employ a frequency dependent shock absorbing apparatus capable of causing a high degree of attenuation of the time-varying components of the shock pulse while causing only a minimal attenuation of the DC valued normal ink flow term.